1. Field of the Invention
This invention relates to a developer device in a printer, photocopier or similar, to an image forming apparatus, and to a toner replenishment method in a developer device, and in particular relates to a developer device which forms an image by using a two-component developer comprising a toner and a carrier to develop an electrostatic latent image formed on an image-carrying member, as well as an image forming apparatus and a toner replenishment method in a developer device.
2. Description of the Related Art
In electro photographic image forming apparatuses, an electrostatic latent image formed on a photosensitive drum using a two-component developer comprising a toner and a carrier is visualized as a toner image, and this toner image is transferred onto recording paper to form an image.
A developer device used in such a two-component development type image forming apparatus is configured, for example, so as to use an agitator to agitate toner supplied to a holding chamber from a cartridge which houses toner, while transporting the toner, and to supply toner which has mixed with the carrier through agitation and which has been friction-charged to a photosensitive drum. That is, toner supplied to the holding chamber is consumed by development of an electrostatic latent image. Hence the developer device comprises a toner concentration sensor which measures the toner concentration in the holding chamber (the ratio of toner to carrier); the toner concentration sensor measures the toner concentration, and supplies toner from the cartridge appropriately based on a voltage value such that the toner concentration in the holding chamber coincides with a target value, to control the toner concentration.